Dial-up is not just for rural areas. There are plenty of suburban areas where I live that are broadband dead-zones - no wireless, no dsl, no cable, no fios. These areas are only a few miles from the city at most. If you look at any internet provider's coverage map, you will see small holes all over the place, and the people living in those holes are just plain out of luck.
There are also a lot of people that can't afford to pay more than $20/mth for internet.
Still, if I ever had to go back to using dial-up for internet, I would give it up entirely.